The Reverse Pull Request

I'm quite confused. I understand why pushing directly to a main branch leads to faster development/deployment iterations, but doing a "reverse pull request" seems to me to be ineffective.

What happens in a situation when someone has some critical feedback in a reverse pull request? It's not like they can suggest changes and block the deployment after the fact. This seems super important for more tenured team members who may have a better understanding of the wider affects a change could bring to a different microservice.

Secondly, why review reverse pull requests? The change is already deployed, and there's likely to be too many to keep on top of for general informational purposes.